The present invention relates to an optical pickup device for carrying out reproduction of an optical recording medium such as a CD, and more particularly to an optical pickup device which can cause an intensity distribution center of a laser beam emitted from a laser beam source to be coincident with an optical axis of an optical system with high precision.
An optical system of an optical pickup device for carrying out reproduction and recording for an optical recording medium such as a CD generally comprises a laser diode 1, a collimate lens 2 for causing a laser beam 11 emitted from the laser diode 1 to be a parallel beam, an uprighting mirror 3 for uprighting the parallel laser beam, and an objective lens 5 for converging, as an optical spot, the laser beam uprighted by the mirror 3 and led on a recording face of an optical disk 6 through an aperture 4 as shown in FIG. 4A. A laser return beam reflected by the optical disk 6 is returned through the same path and is led to a photodetector (not shown) via a half mirror (not shown) provided between the collimate lens 2 and the laser diode 1 so that reproduction information included therein is detected.
An intensity distribution of the laser beam emitted from the laser diode 1 almost represents a Gaussian distribution and has an ellipsoidal shape 11b with maximum and minimum radiation angles of xcex8v and xcex8h in an orthogonal direction as shown in FIG. 5. In general, a central portion of the distributed light 11a shown in an oblique line is utilized through the aperture 4.
As shown in FIGS. 4A and 4B, the center of the intensity distribution of the laser beam 11 should be coincident with an optical axis L of an optical system which passes through an optical axis of an objective lens constituting the optical system. If the center is not coincident with the optical axis L, for example, if the radiation angle of the central distributed light 11a is shifted by xcex8 from the optical axis of the optical system as shown in FIGS. 4C and 4D, the intensity distribution center on the aperture 4 of the objective lens is shifted by xcex94x. As a result, there are drawbacks that a distortion is generated on an optical spot formed on the optical disk, an offset is generated through a push-pull method, a Wobble S/N ratio is deteriorated and lens shift characteristics are imbalanced.
As shown in FIG. 6, a shift of the intensity distribution center of the laser beam 11 in a direction (L3) toward a smaller distribution of the light quantity (FIG. 6A) has a greater influence than a shift in a direction (L4) toward a large distribution of the light intensity (FIG. 6B).
The intensity distribution center of the laser beam is thus shifted from the optical axis of the optical system due to precision of parts of the laser diode or an assembling error. In order to eliminate such a shift of the optical axis, conventionally, Japanese Patent No. 42835778 has disclosed a mechanism for causing the intensity distribution center of the laser beam to be coincident with an optical axis of an optical system by attaching a laser diode to a device frame through an adjusting table and adjusting an angle of a plane in the adjusting table where the laser diode is to be attached with respect to the optical axis of the optical system, for example.
In such a shift adjusting method, however, it is necessary to provide the adjusting table for the laser diode separately. Consequently, a great deal of time and labor is required for the assembly and a cost is increased. Furthermore, the dimension of the device is increased and the structure thereof is also complicated.
In consideration of such a respect, it is an object of the invention to propose an optical pickup device capable of causing the intensity distribution center of a laser beam to be coincident with an optical axis of an optical system with a simple structure.
In order to achieve the above object, according to the present invention, there is formed on a device frame an attachment portion to which a laser diode can be rockably attached. Accordingly, it is possible to carry out such adjustment as to cause the intensity distribution center of the laser beam emitted from the laser diode to be coincident with the optical axis of the optical system without using another member such as the above laser diode adjusting table.